"Isn't being a vegan but having a carnivore boyfriend or girlfriend one of the most hypocritical things a person can do ?"
No it isn't being hypocritical if one truyly loves the other whether one is a vegan and the other eats meat, to have either a boyfriend/girlfriend or a spouse that's not a vegan. It's far more hypocritical to place condsitions on the love of another. A good relationship is based on far more than dietary beliefs. It's based first on love or a deep caring of the other person. Then a willingness to make compromises on the part of both. Also with truly loving the other per8son it means putting aside things such as diet and personal lifestyle beliefs/followings. Only those who are superficial and/or selfish, will place conditions/expectations/requirements on the other person. I spent twenty one years with my late girlfriend before she passed away. When she lost both legs, I didn't leave, because I loved her enough to not leave. Holding back her wheelchair on a steep ramp or other steep incline resulted in my developing an umbilical hernia, and if I had to do over again, I'd not hesitate to risk it again.
Also I knew a couple where she was the vegan and he wasn't. two before we each moved to a different npart of the country had been together for over fifteen years. However she was a registered medical dietitian and before that a registered nurse. She placed his health as a very important part of both his and her life, and loved him enough, that with the problems wouldn't allow him to follow the strict vegeetarian diet that vegans follows.
In the end again it boils down to the most hypocritical thing to do in a relationship, is the placements of conditions on the other person, and done supposedly in the name of love for the pother person.